The present invention relates to apparatus for treating a gas stream. The invention finds particular application in the treatment of a gas stream exhaust from a process chamber used in the semiconductor or flat panel display industry.
A primary step in the fabrication of semiconductor devices is the formation of a thin film on a semiconductor substrate by chemical reaction of vapour precursors. One known technique for depositing a thin film on a substrate is chemical vapour deposition (CVD), which is commonly plasma enhanced. In this technique, process gases are supplied to a process chamber housing the substrate and react to form a thin film over the surface of the substrate. Examples of gases supplied to the process chamber to form a thin film include, but are not restricted to: Silane and ammonia for the formation of a silicon nitride film; Silane, ammonia and nitrous oxide for the formation of a SiON film; TEOS and one of oxygen and ozone for the formation of a silicon oxide film; and AI(CH3)3 and water vapour for the formation of an aluminium oxide film.
Gases exhausted from a process chamber can be treated with high efficiency and at a relatively low cost using a plasma abatement device. In the plasma abatement process, the gas stream is caused to flow into a high density plasma and under the intensive conditions within the plasma species within the gas stream are subjected to impact with energetic electrons causing dissociation into reactive species which can combine with oxygen or hydrogen to produce relatively stable by-products.
During the plasma abatement of gases that produce solid by-products (for example, silica during silane or TEOS oxidation), blockage problems have been encountered in the reaction chamber located down stream of the plasma flare. The chamber typically consists of a pipe of approximately 30 mm in diameter and 90-150 mm in length. The purpose of the reaction chambers is to contain the hot gases in a restricted volume to allow abatement reactions to occur. However, the chamber may become blocked with for example silica particles adhering to the interior surface when abating for example silane, TEOS or organosilanes.
One way of avoiding the adhesion of particles to the walls of the chamber is to form a water weir over their surface. However, there are nevertheless “dry” areas of the plasma reactor between the electrode (anode) and the reaction chamber, and the electrode itself requires additional cleaning.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.